Aircraft automatic braking system

ABSTRACT

An aircraft automatic braking system utilizing the forward wheels of an aircraft landing gear truck for generating signals representative of wheelspeed for utilization in wheelspeed spinup detector circuits in the system while utilizing the rear wheels of the aircraft landing gear truck for generating signals representative of deceleration further compared with selected deceleration to adjust system pressure. To compensate for varying runway conditions, the velocities of a plurality of rear wheels are averaged in providing the signals representative of deceleration.

United States Patent [191 1111 3,920,282

DeVlieg Nov. 18, 1975 {54] AIRCRAFT AUTOMATIC BRAKING 3,767,271 10/1973Grosseau 303/21 F SYSTEM 3,807,810 4/1974 Yarber 244/111 [75] Inventor:Garrett H. DeVlieg, Bellevue, Wash. Primary yg M B [73] Assignee: TheBoeing Company, Seattle, Assistant EXaminer-Douglas C. Butler Wash.Attorney,- Agent, or Firm-Conrad O. Gardner; Glenn 22 Filed: J ne 7,1974 O v 1211' Appl. No.: 477,244 [57] ABSTRACT Related Application D Anaircraft automatic braking system utilizing the for- Division Of Sen394,890 p 6, 1973- .ward wheels of an aircraft landing gear truck forgenerating signals representative of wheelspeed for utili- 303/21 303/ 6R zation in wheelspeed spin-up detector circuits in the II.- CLZ ystemutilizing the rear wheels of the aircraft Fleld of Search F, 61*63,landing gear uck for generating ignals representa- 303/6869, 6 R;188/181 A, 345; 244/111 tive of deceleration further compared withselected deceleration to adjust system pressure. To compensate [56]References Cited for varying runway conditions, the velocities of a plu-UNITED STATES PATENTS rality of rear wheels are averaged in providingthe sig- 3,702,713 11/1972 Oberthur 303/21 F nals representative Ofdeceleration- 3,704,045 11/1972 Walsh t 303/21 F 3,749,451 7/1973 Edsall188/345 x 6 Clams 8 D'awmg F'gures HYMAUL/C sum AUTOMATIC BMK/NGCl'JNTlysL VALVE fill/THE MIL VE ff g c/Acwr muss J20 [1 P MU 118 no //3l/ 02 us US. Patent Nov. 18, 1975 Sheet30f5 3,920,282

US. Patent Nov. 18, 1975 Sheet40f5 3,920,282

AIRCRAFT AUTOMATIC BRAKING SYSTEM This is a division of application Ser.No. 394,890, filed Sept. 6, 1973.

This invention relates to automatic braking systems for aircraft andmore particularly to an automatic braking system for processingwheelspeed signals from the front wheels of landing gear trucks forproviding system energization while utilizing signals representative ofdeceleration developed from aft wheels of the trucks. The systemutilizes a single control valve which meters braking pressure to theshuttle valves (one for each side of the aircraft). The pressure is thenpassed through the shuttle valve to the metered brake pressure line. Thesingle control valve assures equal braking on all wheels, and the twoshuttle valves permit the pilot to instantly override automatic brakingat all times. Normal antiskid control is retained and hydraulic pressuremodulation rates are controlled so that smooth braking is realized andanti-skid efficiency optimized. An orifice in the automatic brakingsystem hydraulic return line is sized to assure smooth release ofautomatic braking not dependent upon electrically generated off rampcontrol signal generating circuits as shown in the system of applicationSer. No. 200,092 filed Nov. 18. 1971 by Glasenapp et al. whichapplication is assigned to the assignee of the present application. Thepresent automatic braking system further permits braking only when thesystem control logic is satisfied.

The importance of avoiding possible runway overrun by prompt brakeapplication after touchdown has been recognized earlier in theaforementioned patent application wherein an automatic braking systemfor reducing the probability of such incidents occurring was provided byautomatically applying wheel braking and decelerating the aircraft at apredetermined rate of deceleration.

The feature of the present system is the utilization of the average of aplurality of forward wheels on aircraft landing gear trucks to providelogic information signals to the system control logic circuits whichprovide the turn on and turn offlogic for the automatic braking system.D. C. wheelspeed signals developed for anti-skid circuit control areprocessed to provide turn on logic and also processed to providepressure control in the control channel.

The present system provides means for averaging a plurality ofwheelspeed signals developed from transducers on a respective pluralityof rear wheels of the landing gear trucks with subsequent signalprocessing including differentiation, filtering and limiting to providesignals which are then compared to signals representative of selecteddeceleration to provide an initial commanded deceleration rate at leastseveral times the selected rate of deceleration (e.g. 5 times) withconsequent decay in commanded deceleration rate to the selected valve ina predetermined time period e.g. onethird second. The error signal issubsequently limited to (nominally) plus or minus 500 psi per second,then coupled through integrator and limiter circuit means furtherlimiting to (nominally) 1800 and 300 psi. The brake pressure controlsignal thus developed in the control channel is then coupled to poweramplifier means and the amplified brake pressure control signal is thencoupled to the automatic brake pressure modulating valve means.

The valve means in accordance with an embodiment of the invention ismounted in a valve module with an 2 upstream solenoid shutoff valve andtwo pressure switches. The valve means meters the automatic brakingpressure to two shuttle valves, one for the brakes on the respectivesides of the aircraft. The pressure is transmitted through the shuttlevalves and the antiskid valves to the brakes, unless the pilots meteredpressure exceeds and overrides the auto-brake pressure at the shuttlevalve. To avoid degrading of anti-skid braking efficiency and to furtherinsure smooth braking. the

, aforementioned rate limits (plus or minus 500 psi/sec nominal) areprovided to prevent rapid pressure variations and the final auto-brakeshutoff. A further important feature of the present automatic brakingsystem is the arrangement of an orifice in the auto-brake valve modulereturn line to cause auto-brake (automatic braking) pressure to bereleased smoothly and rapidly when shut off.

The automatic braking system in the aformentioned application toGlasenapp et al requires that auto brakes must be both hydraulically andelectrically disconnected to permit manual braking override. Also twopressure comparators (hydraulic differential pressure switches) areadded, in addition to the two switches per brake pedal, to sense whenthe pilots metered pressure equals braking pressure then shutting offthe autobrakes. In the Glasenapp et al. system, some passenger joltoccurs during transition from automatic to manual braking since when oneside of the aircraft senses transition by the pressure comparator thenboth sides of the aircraft lose auto-brakes.

The above mentioned disadvantages of the Glasenapp et al. system areovercome in the present system in which automatic braking pressure isregulated by the pressure control valve in the auto-brake module. Thispressure is transmitted through one shuttle valve on each side of theaircraft and into the metered pressure line. Metered pressure switchesmay be utilized to replace the switches on the pilots pedals. Theauto-brake valve module may according to an embodiment of the presentsystem include in series path a solenoid valve, a pressure switch, apressure control valve, and a further pressure switch. The solenoidvalve turns hydraulic power on in the auto brake system, and thepressure control valve in the series path regulates auto brake pressure.Pressure switches for logic detection of critical failures may beincluded in the series path. The present system utilizes less componentsthan the aforementioned Glasenapp system and provides simplified andimproved auto brake control.

Accordingly the objects of the present invention are to provide anautomatic braking system having the following features or advantages:

1. Provision for manual braking override of autobraking even if the autobrakes remain in the on condition both electrically and/orhydraulically.

2. A system design not requiring the utilization of pressurecomparators.

3. The assurance of substantially equal braking on all wheels,independent of anti-skid valve tolerances or valve calibration drift.

4. Minimization of passenger jolt during auto-tomanual reversion of eachside of the aircraft separately.

5. Exclusion of anti-skid control commands from the auto brake commandcontrol path.

6. Elimination of electrical failures as a cause of assymetric braking.

7. Prevention of degradation of anti-skid braking efficiency during autobraking.

A further feature of the present invention is the utilization of adeceleration overshoot command to insure pilot feel of braking attouchdown.

Yet a further feature of the present system comprises the utilization oflimiting circuit means in the automatic brake pressure control signalchannel for limiting the rate of change of auto-brake pressure commandto (nominally plus or minus 500 psi/sec) give smooth brake modulation.

Another feature of the present system comprises the averaging of aplurality of rear truck wheel D. C. level wheelspeed signals (such asthose developed for and utilized in anti-skid signal processing) fordevelopment of signals representative of deceleration and theutilization of front truck wheel D. C. level wheelspeed signals forcoupling to spin-up detection logic to insure that the decelerationmeasuring rear wheel signals are fully spun up by the time the spin-updetecting wheels pass the spin-up detection threshold.

Preferred embodiments of the present invention are described andillustrated in the attached drawings, wherein:

FIG. 1 is a schematic diagram of a preferred embodiment of an aircraftautomatic braking system showing signal processing for developing brakepressure control signals, amplification thereof and an exemplaryhydraulic system coupled thereto for purposes of illustration of acomplete system;

FIG. 2 is a further embodiment ofa hydraulic portion useful in thesystem of FIG. 1 for coupling to the brake pressure control signalsdevelopedtherein instead of the hydraulic portion shown in FIG. 1;

FIG. 3 is illustrative of another hydraulic system which may be coupledto the amplified pressure control signals developed in the controlchannel of FIG. 1;

FIG. 4 is illustrative of yet a further hydraulic system which may becoupled to the amplified pressure control signals developed in thecontrol channel of FIG. 1;

FIG. 5 is illustrative of a side view of a landing gear truckarrangement useful for coupling to wheelspeed deceleration signalgenerating circuit means and wheelspeed spinup detector circuit means ofthe system of FIG. 1 to provide these information signals useful insignal processing in the system of FIG. 1;

FIG. 6 is illustrative of a side view of a multiple wheeled main landinggear truck at the instant of touchdown of the aircraft;

FIG. 7 is also illustrative ofa side view of the truck of FIG. 6 at asubsequent time during the landing sequence when the rear and forwardwheels of the truck are in contact with the runway surface; and,

FIG. 8 is a graph of wheelspeed information signals versus time of thefront and rear wheels of the landing gear truck during the periodsubsequent to touchdown helpful in understanding how decelerationcontrolled braking is provided in automatic braking systems such asshown in FIG. 1.

Turning now to the automatic braking system of FIG. 1, it will be notedthat the pilot prepares the present control system for automaticbrakingprior to landing by closing the pilot arming switch 10 thereby supplyingD. C. power to system logic control circuit means 13 and also byrotating deceleration level selecting switch means 14 to thedeceleration level desired. Upon selection of a desired decelerationlevel, a pilots deceleration command signal 68 is generated through thecoupling ofa positive reference potential to one ofa plurality ofcalibrated resistors shown in deceleration level tem coupled forpurposes ofillustration to a single main gear wheel disposed on eachside of the aircraft, left and right wheelspeed signals 54 and 55 areobtained from the respective left and right anti-skid control circuitmeans and 51 which develop and utilize such signals in a known manner.These left and right wheelspeed signals 54 and 55 are both coupledrespectively to wheelspeed deceleration signal generating circuit means28 and wheelspeed spinup detector circuit means 29. In thecircuit-embodiment of FIG. 1, wheelspeed deceleration signal generatingcircuit means 28 I averages left and right wheelspeed signals 54 and 55and further differentiates the average of the wheel? speeds and furtherfilters out high frequency perturbations to provide a wheel/aircraftdeceleration signal 56 representative of the average deceleration ofleft and right wheels 46 and 47. wheelspeed spinup detector circuitmeans 29 in this circuit embodiment averages. v

left and right wheelspeed signals 54 and 55 and further compares theaverage signal to a predetermined wheelspeed spinup level thereby actingas a switching means to provide a wheelspeed spinup signal 57 having anegative potential level prior to predetermined wheelspeed spinup leveldetection and having a positive reference potential subsequent todetection of the predetermined wheelspeed spinup level.

Turning now to system logic control circuit means 13, it will be notedthat a system logic control signal 63 is developed at the output ofsystem logic control circuit means 13 which is coupled to system logiccontrolled switching means 12. In the presence of a plurality oflogicsignals59, 60, and 61 representative respectively of a plurality ofaircraft operating parameters and wheelspeed spinup signal 57, systemlogic control sig nal 63 aetuates system logic controlled switchingmeans 12 thereby coupling brake application enabling power 65 tohydraulic power shutoff valve means 36 of automatic braking controlvalve means 35 causing opening of shutoff valve means 36. Upon openingof shutoff valve means 36, hydraulic power is transmitted to automaticbraking pressure modulating mvalve means 37, and now brake pressurecontrol signal power I amplifier 26 which couples automatic brakingpressure regulating power 74 to automatic braking pressure modulatingvalve means 37 can provide automatic braking pressure 78 at the outputof automatic braking control valve means 35. System logic controlcircuit means 13 comprises e.g. an AND circuit which provides systemlogic control signal 63 when logic input signal 59 representative of theoutput of the aircraft Air/Ground Mode switch signal, absence of advanceof throttle representative logic input signal 60,logic input signal 61representative of absence of a pilot's brakepedal application, andwheelspeed spinup signal 57 are all present. Upon actuation of systemlogic controlled switching means 12 by system logic control signal 63,deceleration control circuit enabling signal 66 comprising a D. C. levelreference potential is coupled to initial aircraft decelerationovershoot command signal circuit generating means 16 and further coupledto maximum brake pressure control signal limiting circuit means 24portion of deceleration error signal integrating and pressure controlsignal limiting circuit means 22 thereby permitting circuit means 22 tomodulate brake pressure control signal 73 from an initial value as setby minimum brake pressure control signal limiting means 24 to asubsequent value in the control channel necessary to maintain theaircraft deceleration rate selected by the pilot and as commanded by theinitial aircraft deceleration overshoot comm-and signal circuitgeneratingmeans 16.

After automatic braking has been initiated, the aircraftdecelerationerror signal generating and amplitude limiting circuit means 18 adds theinitial aircraft deceleration overshoot command signal 69 to thepreviously selected pilots deceleration command signal 68, the sum ofwhich comprises the net aircraft deceleration command, and furthersubtracts from that sum the wheel/aircraft deceleration signal 56 togenerate an aircraft deceleration error signal 71 which isrepresentative of the magnitude and polarity of the difference betweenthe commanded and actual deceleration levels, and further limits theaircraft deceleration error signal 71 to maximum positive and negativevalues with the deceleration error limiting circuit means 19 and 20,respectively. The aircraft deceleration error signal 71 is then coupledto the deceleration error signal integrating and pressure control signallimiting circuit means 22 which integrates this signal to generate abrake pres sure control signal 73, and further limits the brake pressurecontrol signal 73 to predetermined maximum and minimum values with themaximum and minimum brake pressure control signal limiting circuit means23 and 24, respectively. The brake pressure control signal is thencoupled to the brake pressure control signal power amplifier means 26which generates the automatic braking pressure regulating power 74representative of the brake pressure control signal 73, and theautomatic braking pressure regulating power 74 is then 'coupled to thebrake pressure control valve 37 portion of automatic braking controlvalve means 35 which generates an automatic braking pressure 78 which isrepresentative of the automatic braking pressure regulating power 74 andthereby representative of the brake pressure control signal 73. It cannow be seen that since the automatic braking pressure 78 isrepresentative of the brake pressure control signal 73 and since themaximumand minimum brake pressure control signal limiting circuit means23 and 24 portion of the deceleration error signal integrating andpressure control signal limiting circuit means 22 limits the maximum andminimum values of the brake pressure control signal 73, then the maximumand minimum brake pressure control signal limiting circuit means 23 and24, respectively, can be set and adjusted to limit the maximum andminimum values respsectively which the automatic braking pressure 78 canobtain during automatic braking. Also, it can be now seen that since thebrake pressure control signal 73 is the integral of the airplanedeceleration error signal 71, then the amplitude and polarity of theairplane deceleration error signal 71 is representative of the positiveor negative rate of change of the brake pressure control signal 73 andconsequently the positive and negative rate of change of the automaticbraking pressure 78. Therefore, the deceleration error limiting circuitmeans 19 and portions of the airplane deceleration error signalgenerating and amplitude limiting circuit means 18 in effect can be setand adjusted to limit respectively the maximum positive and negativerate of change of automatic braking pressure 78 during automaticbraking. Finally, it can now be observed that aircraft decelerationovershoot command signal circuit generating means 16 operates in such amanner as to cause an initially high deceleration overshoot commandsignal 69 at the summing input to the aircraft deceleration error signalgenerating and amplitude limiting circuit means 18 when the system logiccontrolled switching means 12 is first actuated, and then causes theinitial deceleration overshoot command signal 69 to decay with time(exponentially in this embodiment) to zero, and thereby the initialdeceleration overshoot command signal 69, being added to the pilotsdeceleration command signal 68 as selected by the pilot with thedeceleration level selecting switch means '14, causes a net aircraftdeceleration command that is initially high and then decays(exponentially) to the level selected by the pilot for the remainingoperation of the automatic braking system, thereby giving the pilot acertain feel" when automatic braking is first applied. It should benoted that the rate of application of automatic braking pressure 78caused by this initial deceleration overshoot command signal 69 islimited to the rate as set by the deceleration errorlimiting circuitmeans 19 and 20 portions of the airplane deceleration error signalgenerating and amplitude limiting circuit means 18 as previouslydescribed.

Turning now to the hydraulic portion of the system, a simplifiedembodiment of which is depicted herein in FIG. 1 for illustrativepurposes, hydraulic fluid is supplied to the left and right pilots pedaloperated pressure metering valve means 33 and 34, respectively, and oneautomatic braking control valve means 35. The left and right pilotspedal operated pressure metering valve means 33 and 34, respectively,each in known manner generate a left and right pilot's metered brakingpressure 76 and 77, respectively, which is representative of the forcewith which the pilot applies his left and right, respectively, pilotsbrake pedal means 31 and 32. The automatic braking control valve means35 generates an automatic braking pressure 78 in the manner previouslydescribed to regulate airplane deceleration. Also, in accordance withthis hydraulic embodiment, the automatic braking control valve means 35incorporates an hydraulic fluid restrictor means 38 in the automaticbraking pressure modulating valve return line 39 which slows down therelease of hydraulic fluid from the automatic braking pressure 78through the automatic braking control valve means 35 to the hydraulicreturn line, thereby insuring a gradual and comfortable release ofautomatic braking pressure 78 when the automatic braking system isturned off. Now, noting the operation of the left hand side of thehydraulic system and observing that the right hand side operates in anidentical manner with the single automatic braking pressure 78 beingcommon to both sides, the left pilots metered braking pressure 76 iscoupled to one input port of the left shuttle valve 40 and the automaticbraking pressure 78 is connected to the other input port of the leftshuttle valve 40. Left shuttle valve 40 then compares the two inputpressures, left pilots metered braking pressure 76 and automatic brakingpressure 78, and blocks the lower of the two input pressures whilepermitting the higher of the two input pressures to freely pass throughthe left shuttle valve 40 to become the left metered braking pressure80. For example, during auto- 7 matic braking when the left pilotsmetered braking pressure 76 is lower than the automatic braking pressure78 the left shuttle valve 40 blocks the left pilots metered brakingpressure 76 and allows the automatic braking pressure 78 to freely passthrough the left shuttle valve 40 to become the left metered brakingpressure 80. Then when the pilot applies sufficient left pilots meteredbraking pressure 76 to exceed the automatic braking pressure 78, leftshuttle valve 40 blocks the automatic braking pressure 78 and allowsleft pilots metered braking pressure 76 to freely pass through leftshuttle valve 40 to become left metered braking pressure 80. Leftmetered braking pressure 80 is then coupled to left anti-skid valve 42which generates left brake pressure 82 as commanded by left anti-skidvalve signal 88. Left brake pressure 82 is then coupled to left brake 44which applies braking torque to left wheel 46. For illustrative purposesherein, a left anti-skid wheelspeed transducer 48 continuously generatesa left raw" wheelspeed signal 85 in known manner which is representativeof the rolling speed of left wheel 46. Left raw wheelspeed signal 85 isthen coupled to the left anti-skid control circuit 50 which, in knownmanner, generates a left wheelspeed signal 54 to be representative ofthe rolling speed of left wheel 46 and also generates a left anti-skidvalve signal 88 which is in turn coupled to the left anti-skid valve 42.

The anti-skid system comprises left anti-skid wheelspeed transducer 48,left anti-skid control circuit 50, and left anti-skid valve 42. Leftanti-skid control circuit 50 continually monitors left raw wheelspeedsignal 85 from left anti-skid wheelspeed transducer 48 to generate theleft wheelspeed signal 54 and then continually monitors the leftwheelspeed signal 54 to determine whether the left wheel 46 is skidding.If the left antiskid control circuit determines that no skid activityexists, then the circuit transmits a left anti-skid valve signal 88 tothe left anti-skid valve 42 causing it to freely pass the left meteredbraking pressure 80 through the valve and become the left brake pressure82. If the left anti-skid control circuit 50 determines that skidactivity does exist, then the circuit transmits a left anti-skid valvesignal 88 to left anti-skid valve 42 causing it to reduce the left brakepressure 82 by some variable amount below the level of the left meteredbraking pressure 80, thereby correcting the skidding condition of leftwheel 46.

During typical operation of the automatic braking system, it can be seenthat when the left and right brake pressures 82 and 83 are notsufficiently high to cause wheel skids, the automatic braking pressure78 at the output ofthe automatic braking control valve means 35 wouldpass freely through both the left and right shuttle valves 40 and 41 andthe left and right anti-skid valves 42 and 43 to become the left andright brake pressures 82 and 83, respectively. Left and right brakepressures 82 and 83 exert a braking force to the left and right wheels46 and 47 causing the aircraft to decelerate. Since the left and rightwheels 46 and 47 are assumed not be in a skid condition, the rollingspeed of the wheels is substantially representative of the aircraftvelocity and therefore the wheel/aircraft deceleration signal, which isgenerated by wheelspeed deceleration signal generating circuit means 28to be the derivative of the average of the left and right wheelspeedsignals 54 and 55, is substantially representative of the rate ofaircraft deceleration. This wheel/aircraft deceleration signal 56 isthen compared by the aircraft deceleration error signal generating andamplitude limiting means 18 to the sum of the pilots decelerationcommand sig nal 68 and the initial deceleration overshoot command signal69 to generate an aircraft deceleration error signal 71. The aircraftdeceleration error signal 71 is then integrated by deceleration errorsignal integrating and pressure control signal limiting circuit means 22to generate brake pressure control signal 73 which in turn causes thebrake pressure control signal power ampli-.

fier means 26 .and automatic braking pressure modulating valve means 37to generate an automatic braking pressure 78 and consequent left andright brake pres- I sures 82 and 83, respectively, which arerepresentative of the brake pressure control signal 73. When theaircraft deceleration error signal generating and amplitude limitingcircuit means 18 detects an aircraft deceleration level, as representedby the wheel/aircraft deceleration signal 56, which is less than thecommanded deceleration level, as represented by the sum of the pilotsdeceleration command signal 68 and the initial deceleration overshootcommand signal 69, the resulting aircraft deceleration error signal 71causes deceleration error signal integrating and pressure control signallimiting circuit means 22 to increase the automatic braking pressure 78,and thereby left andright brake pressures 82 and 83, respectively, at arate which is representative of the amplitude of the aircraftdeceleration error signal 71, the rate being limited by decelerationerror signal limiting circuit means 19, thereby causing an increase inaircraft deceleration as represented by sure control signal limitingcircuit means 22 to decrease the automatic braking pressure 78, andthereby the left and right brake pressures 82 and 83, respectively, at arate which is representative of the amplitude.

of the aircraft deceleration error signal 71, the rate being limited bydeceleration error signal limiting circuit means 20, thereby causing adecrease in aircraft deceleration, as represented by the wheel/aircraftdeceleration signal 56, and a decrease in the magnitude of the aircraftdeceleration error signal 71.

If wheel skidding begins to occur, left and right antiskid controlcircuit means 50 and 51, respectively, cause left and right anti-skidvalve means 42 and 43,

respectively, to reduce left and right brake pressures 82 and 83,respectively, below the automatic braking pres sure 78 and therebyprevent or correct a sudden decrease in left and right wheelspeedsignals 54 and 55,

respectively. This reduction of the left and right brake pressures 82and 83 causes the aircraft deceleration, as

represented by the wheel/aircraft deceleration signal,

to be reduced. The effects of any momentarily sharp decreases andincreases in speed of the left and right 7 wheels 46 or 47,respectively, as caused by anti-skid I generating circuit means 28 andby the cancelling effect of the high deceleration that occurs as thewheel goes into'a skid followed by the high acceleration that occurs asthe wheel recovers from the skid. Therefore, even during wheel skidactivity, the wheel/aircraft deceleration signal 56 is substantiallyrepresentative of the actual aircraft deceleration, so, when left andright brake pressures 82 and 83, respectively, have been lowered by theanti-skid system due to skid activity, the resulting decrease inaircraft deceleration, as represented by the lower wheel/aircraftdeceleration signal 56, causes automatic braking pressure 78 toincrease. Since left and right anti-skid control circuit means 50 and51, respectively, will not allow the increased automatic brakingpressure 78 to cause an increase in left and right brake pressures 82and 83, respectively, beyond the level which causes skid activity, thecondition of low aircraft deceleration persists despite the increase inautomatic braking pressure 78, and so the automatic braking pressure 78continues to rise until either the aircraft deceleration reaches thecommanded level or the automatic braking pressure 78 reaches the levelset by the maximum brake pressure control signal limiting circuit means23 portion of deceleration error signal integrating and pressure controlsignal limiting circuit means 22.

During anti-skid braking, the limits on automatic braking pressure 78rate of change, as set by deceleration error circuit limigint means 19and 20 portion of the airplane deceleration error signal generating andamplitude limiting circuit means 18, as previously described, preventsudden changes in automatic braking pressure 78 which might interferewith the anti-skid systems ability to efficiently control skid activity,and therefore, the said rate limits insure that the automatic brakingsystem will not degrade aircraft stopping ability during anti-skidcontrolled braking. Also, the present limit on maximum automatic brakingpressure 78, as set by maximum brake pressure control signal limitingcurcuit means 23 portion of the deceleration error signal integratingand pressure control signal limiting circuit means 22 in the mannerpreviously described, prevents the automatic braking pressure 78 fromreaching such a high level as to degrade the anti-skid systems abilityto efficiently control skid activity, and therefore the maximum pressurelimit insures that the automatic braking system will not degradeaircraft stopping ability during anti-skid controlled braking. Theaforementioned maximum pressure limit would normally be preset to a highenough level to permit the automatic braking pressure 78 to reach a highenough level to cause the commanded deceleration level to be achievedduring conditions where no anti-skid activity exists.

Finally, when the automatic braking system is disengaged by the pilot,normally by the application of the left and right pilots brake pedalmeans 31 and 32, respectively, a logic signal, typically the pilotsbrake pedal application signal 61, is transmitted to the system logiccontrol circuit means 13 which in turn de-energizes the system logiccontrolled switching means 12 and thereby decouples the brakeapplication enabling power 65 and the deceleration control circuitenabling signal 66. By removing deceleration control circuit enablingsignal 66, minimum brake pressure control signal limiting circuit means24 portion of the deceleration error signal integrating and pressurecontrol signal limiting circuit means 22 reduces brake pressure controlsignal 73 so that the automatic braking pressure 74 is commanded to arelease condition. and also the initial aircraft deceleration overshootcommand signal circuit generating means 16 is reset to again command aninitial deceleration overshoot command signal 69 when the nextdeceleration control circuit enabling signal 66 is generated. Byremoving the brake application enabling power 65, the hydraulic powershutoff valve means 36 portion of the automatic braking control valvemeans 35 is de-energized which causes the valve means to removehydraulic power from the automatic braking pressure modulating valvemeans 37 portion of the automatic braking control valve means 35, andalso brake pressure control signal power amplifier means 26 isde-energized which in turn removes the automatic braking pressureregulating power 74 which causes automatic braking pressure modulatingvalve means 37 to couple the automatic braking pressure 78 to theautomatic braking pressure modulating valve return line 39.

When the automatic braking pressure 78 is coupled to the automaticbraking pressure modulating valve re turn line 39, the hydraulic fluidrestrictor means 38 causes the automatic braking pressure 78 to releaseat a rate which causes a smooth but noticeable automatic brakingpressure 78 release. Also, as previously described, whenever theautomatic braking pressure drops below the left and right pilots meteredbraking pressures 76 and 77, respectively, left and right shuttle valvemeans 40 and 41, respectively, act to block the automatic brakingpressure 78 and couple the left and right pilot's metered brakingpressures 76 and 77 to the left and right metered braking pressure 80and 81, respectively, thereby placing the entire braking system undernormal pilot control.

The following description relates to FIGS. 2, 3 and 4, wherein there areschematically depicted three embodiments of the hydraulic portion of theautomatic braking system of FIG. 1 useful in three different aircrafthydraulic braking system configurations. FIG. 2 shows the automaticbraking system hydraulic components coupled to an aircraft hydraulicbraking system having a plurality of braked wheels through 107, allbeing serviced by a single hydraulic supply. This embodiment operates ina manner similar to the embodiment of FIG. 1 except that left and rightshuttle valve means 40 and 41 provide left and right metered brakingpressures 80 and 81, respectively, to a plurality of left and rightanti-skid valve means 100, 101, 102 and 103, and 104, 105, 106, and 107,respectively, instead of the single left and right anti-skid valve means42 and 43, respectively, of FIG. 1. Braked wheel now described istypical of the operation of the other braked wheels 111 through 117 inbeing provided with an antiskid wheelspeed transducer means 118, ananti-skid control circuit means 120, and an anti-skid control valvemeans 100 which are coupled together and operate in the mannerpreviously described in connection with the system of FIG. 1 to provideskid protection to braked wheel 110 and to generate a wheelspeed signal122 which is representative of the rotary speed of braked wheel 110, sothat there is a single wheelspeed signal that is generated by eachbraked wheel to be representative of the rotary speed of that respectivebraked wheel. Any number and combination of wheel= speed signals arethen coupled to the wheelspeed deeel= eration signal generating circuitmeans 28 of FIG; I which generates a wheel/aircraft deceleratlofi signal56 representative of the average deceleration of that num= her andcombination of wheelspeed signals, and the same or different number andcombination of wheel speed signals are then coupled to wheelspeed spinupdetector circuit means 29 of FIG. 1 which generates a wheelspeed spinupsignal 57 when the average of said same or different number andcombination of wheelspeed signals exceeds the present spinup threshold.

Now, for example, FIG. 5 shows a main landing gear configuration whereit is advantageous to couple all the wheelspeed signals typical of 204from the rear wheels typical of 201 on each main landing gear truck beamtypical of 200 to wheelspeed deceleration signal generating circuitmeans 28 of FIG. 1 so that the circuit generates a wheel/aircraftdeceleration signal 56 which is representative of the averagedeceleration of the rear wheels on all the main landing gear truck beamstypical of 200 and further to couple all the wheelspeed signals typicalof 205 from the forward wheels typical of 202 on each main landing geartruck beam typical of 200 to the wheelspeed spinup detector circuitmeans 28 of FIG. 1 so that the circuit generates a wheelspeed spinupsignal 57 when the average speed of the forward wheels on all the mainlanding gear truck beams exceeds the present spinup threshold. By way ofthis embodiment, FIG., 6 shows a side view of a multiple wheeled mainlanding gear at the instant of aircraft touchdown, and shows that themain landing truck beam 200 is biased to tilt upward in flight so thatthe rear wheels typical of 201 contact the runway at touchdown prior tothe forward wheels typical of 202. FIG. 7 shows the same main landinggear a moment later when the aircraft has touched down firmly and boththe rear and forward wheels 201 and 202, respectively, have contactedthe runway. FIG. 8 is an illustrative plot of wheelspeed signal versustime for the rear and forward wheels typical of 201 and 202,respectively, showing that due to the rear wheels contacting the runwayprior to the forward wheels, the rear wheels spin up to a speedsynchronouswith the aircraft velocity prior to the forward wheels. Bycoupling the forward and rear wheelspeed signals typical of 205 and 204,respectively of FIG. 5 to the wheelspeed spin-up detector circuit means29 and the wheelspeed deceleration signal generating circuit means 28,respectively, of FIG. 1, a wheelspeed spin-up signal 57 is not generatedto cause the system to begin to apply deceleration controlled brakinguntil the rear wheelspeeds have achieved or nearly achieved a speedsynchronous with the velocity of the aircraft, thereby minimizing oreliminating the momentary error in the wheel/aircraft decelerationsignal 57 of FIG. 1 caused by initial wheel spin-up. Another advantageof present coupling of the forward and rear wheelspeed signals 205 and204, respectively, to the wheelspeed spin-up detector circuit means 29and the wheelspeed deceleration signal generating circuit means 28,respectively, of FIG. 1, as shown in FIG. 5, is that it is desirablethat most or all of the braked wheels be partly or completely spun upbefore brake pressure is applied so that the anti-skid system canadequately provide skid protection, since if brakes were applied priorto wheel spinup, and if brake pressure were sufficient to cause a wheelskid or prevent spinup, and if no other means were provided to the antiSkid system to know that a locked wheel condition existed, then blowntires would result.

Turning now to FIG. 3, the automatic braking system hydraulic componentsare shown coupled to an aircraft hydraulic braking system having aplurality of braked two automatic braking control valve means and 136and four shuttle valve means 140 through 143 and the left and rightpilots brake pedal means 31 and 32,

respectively, each operate a pair of left and right pilots pedaloperated pressure metering valve means 145 and 146, respectively. Brakedwheel 130 is shown as typical, of the other braked wheels 131, 132, and133 in being provided with an anti-skid wheelspeed transducer I means148, an anti-skid control circuit means 149, and

an anti-skid control valve means 146, which are coupled together andoperate in known manner as previously described to provide skidprotection to braked wheel 130 and to generate a wheelspeed signal 147which is representative of the rotary speed of braked wheel 130, so thatthere is a single wheelspeed signal that is generated by each brakedwheel to be. represen- .tative of the rotary speed of that respectivebraked wheel. Any number and combination of wheelspeed signals are thencoupled to the wheelspeed deceleration signal generating circuit means28 and wheelspeed spin-up detector circuit means 29 of FIG. 1 aspreviously described. The two automatic braking control 1 valve means135 and 136 are coupled to the automatic braking system electricalsystem of FIG. 1 in such a manner that both automatic braking control.valve means 135 and 136 operate substantially identically andsimultaneously with each other to generate equal automatic brakepressures 150 and 151 at all times. For 7 example, the brake applicationenabling power 65 of FIG. 1 could be coupled in parallel to bothhydraulic power shutoff valve means-153 and 154 of FIG. 3 and theautomatic braking pressure regulating power 74 of FIG. 1 could becoupled in series to both automatic braking pressure modulating valvemeans 155 and 156,

and thereby cause the brake application enabling power 65 of FIG. 1 toopen both hydraulic power shutoff valve means 153 and 154 of FIG. 3simultaneously and cause the automatic braking pressure regulating power74 of FIG. 1 to command both automatic braking pressure modulating valvemeans 155 and 156 of FIG. 3 to simultaneously regulate the. automaticbraking pressures 150 and 151, respectively, to be substan I tiallyequal at all times and representative of the automatic braking pressureregulating power.

Turning now to FIG. 4, the automatic braking system hydraulic componentsare shown coupled to an aircraft hydraulic braking system having aplurality of braked. wheels 160 through 167 each being serviced by bothof.

two hydraulic supplies 126 and 128. This embodiment operates in asimilar manner to the embodiment of FIGQ 3 except that each braked wheel160 through 167 containsa brake which is actuated by either or both oftwo.

separate brake pressures so that each braked wheel is serviced by abrake pressure from each hydraulic supply. As in FIG. 2 and 3, a typicalanti-skid control cir cuit is shown for a braked wheel which iseoupledto provide skid protection for the braked wheel and furtherprovides a wheelspeed signal 169 which is representative of the rotaryspeed of braked wheel 160. The

wheelspeed signals typical of 169 are coupled to the 7 electricalcontrol system of FIG. 1 as explained in connection with FIG. 2. Theelectrical control system of FIG. 1 is coupled to the two automaticbraking control valve means 135 and 136 as explained earlier inconnection with the description of FIG. 4.

I claim:

1. An aircraft automatic braking system comprising in combination:

means for generating a brake pressure control signal;

automatic braking pressure modulating valve means responsive to saidbrake pressure control signal for metering automatic braking pressure tofirst shuttle valve means for application to the brakes on one side ofthe aircraft and second shuttle valve means for application to thebrakes on the other side of the aircraft;

first manually controlled pressure metering valve means coupled to saidfirst shuttle valve means and second manually controlled pressuremetering valve means coupled to said second shuttle valve means, each ofsaid first and second shuttle valve means arranged for transmitting thegreater of manually or automatically controlled pressures forapplication to the brakes on the respective sides of the aircraft; and

shutoff valve means for transmitting hydraulic power to said automaticbraking pressure modulating valve means in response to an aircraftoperating parameter.

2. The combination according to claim 1 further including hydraulicfluid restrictor means disposed in the hydraulic portion of said systemfor restricting the release of automatic braking pressure.

3. An aircraft automatic braking system comprising in combination:

means for generating a brake pressure control signal;

automatic braking pressure modulating valve means responsive to saidbrake pressure control signal for metering automatic braking pressure tofirst shuttle valve means for application to the brakes on one side ofthe aircraft and second shuttle valve means for application to thebrakes on the other side of the aircraft; and

first manually controlled pressure metering valve means coupled to saidfirst shuttle valve means and second manually controlled pressuremetering valve means coupled to said second shuttle valve means, eachofsaid first and second shuttle valve means arranged for transmitting thegreater of manually or automatically controlled pressures forapplication to the brakes on the respective sides of the aircraft.

4. The combination according to claim 3 further including hydraulicfluid restrictor means disposed in the hydraulic portion of said systemfor restricting the release of automatic braking pressure.

5. An aircraft automatic braking system comprising in combination:

means for generating a brake pressure control signal;

automatic braking pressure modulating valve means responsive to saidbrake pressure'control signal for metering automatic braking pressure tofirst shuttle valve means for application to the brakes on one side ofthe aircraft and second shuttle valve means for application to thebrakes on the other side of the aircraft;

first manually controlled pressure metering valve means coupled to saidfirst shuttle valve means and second manually controlled pressuremetering valve means coupled to said second shuttle valve means; andplurality of first and second anti-skid valves coupled to the respectiveoutputs of said first and second shuttle valve means. said anti-skidvalves providing for release of brake pressures in the event of skidcontrol of said aircraft.

6. The combination according to claim 5 further including shutoff valvemeans for controlling the transmission of automatic braking pressure tosaid first and second shuttle valve means in response to an aircraftoperating parameter.

1. An aircraft automatic braking system comprising in combination: meansfor generating a brake pressure control signal; automatic brakingpressure modulating valve means responsive to said brake pressurecontrol signal for metering automatic braking pressure to first shuttlevalve means for application to the brakes on one side of the aircraftand second shuttle valve means for application to the brakes on theother side of the aircraft; first manually controlled pressure meteringvalve means coupled to said first shuttle valve means and secondmanually controlled pressure metering valve means coupled to said secondshuttle valve means, each of said first and second shuttle valve meansarranged for transmitting the greater of manually or automaticallycontrolled pressures for application to the brakes on the respectivesides of the aircraft; and shutoff valve means for transmittinghydraulic power to said automatic braking pressure modulating valvemeans in response to an aircraft operating parameter.
 2. The combinationaccording to claim 1 further including hydraulic fluid restrictor meansdisposed in the hydraulic portion of said system for restricting therelease of automatic braking pressure.
 3. An aircraft automatic brakingsystem comprising in combination: means for generating a brake pressurecontrol signal; automatic braking pressure modulating valve meansresponsive to said brake pressure control signal for metering automaticbraking pressure to first shuttle valve means for application to thebrakes on one side of the aircraft and second shuttle valve means forapplication to the brakes on the other side of the aircraft; and firstmanually controlled pressure metering valve means coupled to said firstshuttle valve means and second manually controlled pressure meteringvalve means coupled to said second shuttle valve means, each of saidfirst and second shuttle valve means arranged for transmitting thegreater of manually or automatically controlled pressures forapplication to the brakes on the respective sides of the aircraft. 4.The combination according to claim 3 further including hydraulic fluidrestrictor means disposed in the hydraulic portion of said system forrestricting the release of automatic braking pressure.
 5. An aircraftautomatic braking system comprising in combination: means for generatinga brake pressure control signal; automatic braking pressure modulatingvalve means responsive to said brake pressure control signal formetering automatic braking pressure to first shuttle valve means forapplication to the brakes on one side of the aircraft and second shuttlevalve means for application to the brakes on the other side of theaircraft; first manually controlled pressure metering valve meanscoupled to said first shuttle valve means and second manually controlledpressure metering valve means coupled to said second shuttle valvemeans; and a plurality of first and second anti-skid valves coupled tothe respective outputs of said first and second shuttle valve means,said anti-skid valves providing for release of brake pressures in theevent of skid control of said aircraft.
 6. The combination according toclaim 5 further including shutoff valve means for controlling thetransmission of automatic braking pressure to said first and secondshuttle valve means in response to an aircraft operating parameter.